As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of secondary batteries has also sharply increased as an energy source for the mobile devices. One of the secondary batteries is a lithium secondary battery having high energy density and discharge voltage, on which much research has been carried out and which is now commercially and widely used.
However, various combustible materials are contained in the lithium secondary battery. As a result, there is a possibility of danger in that the lithium secondary battery can be heated or explode due to overcharge, overcurrent, or any other external physical impacts. In other words, the lithium secondary battery has low safety. Consequently, a protection circuit module (PCM) for effectively controlling the abnormality of the lithium secondary battery, such as overcharge, is mounted in the lithium secondary battery while the PCM is connected to a battery cell of the lithium secondary battery.
The PCM includes a field effect transistor (FET), which serves as a switching element for controlling electric current, a voltage detector, and passive elements such as a resistor and a capacitor. The PCM interrupts overcharge, overdischarge, overcurrent, short circuits, and reverse voltage of the battery to prevent the explosion or the overheating of the battery, the leakage of liquid from the battery, and the degradation of the charge and discharge characteristics of the battery, and to suppress the lowering of the electrical efficiency of the battery and the abnormal behavior of the battery, thereby eliminating dangerous factors from the battery and increasing the service life of the battery.
Generally, the PCM is connected to the battery cell via conductive materials, such as nickel plates, by welding or soldering, which provides a high coupling strength. However, the welding or soldering process, performed with respect to small-sized devices, such as the battery cell, requires a high degree of technical skill with the result that skilled persons are needed. Also, the welding or soldering process requires a large working space. Furthermore, when physical impacts are applied to the battery cell, an electrical short may occur, and therefore, the battery cell may catch fire or explode. In other words, safety-related problems may occur. In addition, it is required for safety elements, including the PCM, to be maintained in electrical connection with the electrode terminals of the battery cell and, at the same time, to be electrically isolated from other parts of the battery cell. Consequently, a plurality of insulative mounting members are required to construct such connection, with the result that the battery assembling process is complicated.
In connection with this matter, there have been proposed technologies for coupling the PCM to the battery cell without using the conventional welding or soldering in order to solve the problems caused by the welding or soldering. For example, Korean Patent Application Publication No. 2007-0067781 discloses a lithium polymer battery including an electrode assembly, a sheathing member having an internal space for receiving the electrode assembly defined therein, side residual parts extending outward from opposite sides of the internal space, a front residual part extending outward from the front of the internal space, the front residual part being folded in the direction in which the internal space is located (hereinafter, referred to as an ‘upward direction’), and a circuit board disposed at the front of the sheathing member, the circuit board being electrically connected to electrode tabs extending from two electrodes of the electrode assembly, the electrode tabs being partially exposed out of the sheathing member through the front residual part and bent downward.
Also, Korean Patent Application Publication No. 2004-0029757 discloses a secondary battery including a battery cell having a PCM installation space, a PCM for interrupting overcharge, overdischarge, and overcurrent, a pair of terminals disposed at the rear of the PCM, a pair of connection tabs fixed to the respective terminals, a pair of electrode tabs, made of an aluminum plate and a nickel plate, respectively, connected to the electrode plates of the battery cell, one end of each electrode tab being fixed to the corresponding connection tab, wherein the PCM is installed in the PCM installation space such that the front of the PCM is exposed by bending the electrode tabs once.
However, the above-described technologies have problems in that the electrode tabs bent downward from the front of the battery cell sheathing member and connected to the circuit board and the electrode tab pair installed in the PCM installation space, while being bent once, exhibit a low coupling strength with respect to the circuit board and low connection reliability, with the result that contact resistance increases, and therefore, when physical impacts are applied to the battery cell, an electric short circuit occurs, whereby the battery cell may catch fire or explode, i.e., safety-related problems may occur.
Meanwhile, Korean Patent Application Publication No. 2004-0029757 discloses an assembling type PCM including a protection circuit for controlling overcharge, overdischarge, and overcurrent of the battery, wherein a pair of connection members are attached to the bottom of the PCM while being electrically connected to the protection circuit, and the connection members are configured in a groove-shaped connection structure in which plate-shaped electrode terminals of the battery cell are fixedly inserted into the coupling grooves of the respective connection members.
In the above-described connection member, however, it is not easy for the electrode terminals of the battery cell to be inserted into the coupling grooves of the respective connection members, and, when a reliability test, such as a dropping test, is performed, the contact resistance at the coupling regions between the electrode terminals and the connection members may increase, a short circuit may occur, and the coupling grooves may widen.
Consequently, there is a high necessity for a PCM including new-structured connection members that are easy to manufacture, have a simple connection structure, and simultaneously effectively improve the coupling between the battery cell and the PCM and the electrical connection and mechanical coupling between the electrode terminals of the battery cell and the PCM.